Molecular sieve materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain molecular sieves (e.g., zeolites, AlPOs, or mesoporous materials) are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by X-ray diffraction. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as “molecular sieves” and are utilized in a variety of industrial processes. The pores in microporous crystalline molecular sieves normally have a cross section dimension from about 2 Å to about 19 Å. This as opposed to mesoporous molecular sieves which have pore sizes between 20 Å and 1000 Å.
Molecular sieves that find application in catalysis include any of the naturally occurring or synthetic crystalline molecular sieves. Examples of these zeolites include large pore zeolites, intermediate pore size zeolites, and small pore zeolites. These zeolites and their isotypes are described in “Atlas of Zeolite Framework Types”, eds. W. H. Meier, D. H. Olson and Ch. Baerlocher, Elsevier, Fifth Edition, 2001, which is hereby incorporated by reference. A large pore zeolite generally has a pore size of at least about 7 Å and includes LTL, VFI, MAZ, FAU, OFF, *BEA, and MOR framework type zeolites (IUPAC Commission of Zeolite Nomenclature). Examples of large pore zeolites include mazzite, offretite, zeolite L, VPI-5, zeolite Y, zeolite X, omega, and Beta. An intermediate pore size zeolite generally has a pore size from about 5 Å to less than about 7 Å and includes, for example, MFI, MEL, EUO, MTT, MFS, AEL, AFO, HEU, FER, MWW, and TON framework type zeolites (IUPAC Commission of Zeolite Nomenclature). Examples of intermediate pore size zeolites include ZSM-5, ZSM-11, ZSM-22, MCM-22, silicalite 1, and silicalite 2. A small pore size zeolite has a pore size from about 3 Å to less than about 5.0 Å and includes, for example, CHA, ERI, KFI, LEV, SOD, and LTA framework type zeolites (IUPAC Commission of Zeolite Nomenclature). Examples of small pore zeolites include ZK-4, ZSM-2, SAPO-34, SAPO-35, ZK-14, SAPO-42, ZK-21, ZK-22, ZK-5, ZK-20, zeolite A, chabazite, zeolite T, gmelinite, ALPO-17, and clinoptilolite.
Synthetic molecular sieves are often prepared from aqueous reaction mixtures (synthesis mixtures) comprising sources of appropriate oxides. Organic directing agents (“structure directing agent”) may also be included in the synthesis mixture for the purpose of influencing the production of a molecular sieve having the desired structure. The use of such directing agents is discussed in an article by Lok et al. entitled “The Role of Organic Molecules in Molecular Sieve Synthesis” appearing in Zeolites, Vol. 3, October, 1983, pp. 282-291.
After the components of the synthesis mixture are properly mixed with one another, the synthesis mixture is subjected to appropriate crystallization conditions in an autoclave. Such conditions usually involve heating of the synthesis mixture to an elevated temperature possibly with stirring. Room temperature aging of the synthesis mixture is also desirable in some instances.
After the crystallization of the synthesis mixture is complete, the crystalline product may be recovered from the remainder of the synthesis mixture, especially the liquid contents thereof. Such recovery may involve filtering the crystals and washing these crystals with water. However, in order to remove the entire undesired residue of the synthesis mixture from the crystals, it is often necessary to subject the crystals to a high temperature calcination e.g., at 540° C., possibly in the presence of oxygen. Such a calcination treatment not only removes water from the crystals, but this treatment also serves to decompose and/or oxidize the residue of the organic directing agent which may be occluded in the pores of the crystals, possibly occupying ion exchange sites therein.
However, synthetic molecular sieves are expensive. A need exists for a high throughput process of manufacturing molecular sieves. This invention discloses a high throughput process of manufacturing molecular sieves by the combination of high solid content and high temperature. Such method of manufacturing has the advantage of low cost, short crystallization time, and high yield.